Jeff Hoffmann - Nathan BaxterBackground---------------------------------------------------------------------------------

For the past few decades, Scientists have been studying electrochemical processes that

convert carbon dioxide to oxygenates and other simple hydrocarbons such as carbon

monoxide, formic acid, methane, ethylene and ethane, but, as research conducted by Song

et al. points out, these processes have only been capable of producing any one product with

low efficiencies—less than ten percent. In 2016, a group of scientists at the Department of

Energy’s Oak Ridge National Laboratory discovered a process that converts carbon dioxide

to ethanol with a comparatively high selectivity and efficiency—reaching yields of 63

percent. This significant difference in yield makes the process that these researchers

discovered much more practical.

Technology & Chemistry----------------------------------------------------------------------------------------------------------------------------------

This conversion of carbon dioxide to ethanol requires relatively few components: water,

carbon dioxide, electricity, and the specially designed electrodes. In research done by Lim

et al. it is explained how the process breaks down carbon dioxide and allows the

molecules to reassemble as other oxygenates and hydrocarbons. The key to this process

is the specially designed electrode. These electrodes are constructed of a metal-

based catalyst bound to a highly textured graphene surface. The shape of these carbon

nanospikes is crucial to the process’ ability to produce complicated hydrocarbons and

oxygenates. Overall, the process follows the formula:

2 CO2 (aq) + 9 H2O(l) → C2H5OH(aq) + 12 OH -(aq)

(Carbon Dioxide) (Water) (Ethanol) (Hydroxide)

For this to happen, a molecule of carbon dioxide must bond with copper on the carbon

nanospike surface. Once carbon dioxide has bonded to the copper electrode, it is

considered absorbed by the copper. From this point, carbon dioxide can be converted into

many different hydrocarbons and oxygenates; but, beyond this point, the chemical reactions

between carbon dioxide and the water will be different for each product.

Potential Applications-------------------------------------------------------------------------------------------------

Emissions

• Can take the place of fossil fuel sources

• Consumes carbon dioxide

• Reduces the effects of climate change (e.g. global warming and

shifting precipitation patterns) caused by carbon dioxide emissions.

• Promotes sustainable environmental practices

Energy

• Store excess energy produced

• Combat intermittency issues

• Stabilize electrical grid supply and demand

• Promotes sustainable energy handling practices

Food

Supply

• Can take the place of biomass as ethanol production feedstock

• Increase available food supply

• Promotes sustainable food management practices

Example Reaction: Methane (CH4)---------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Step 0:

Step 1:

Step 2:

Step 3,

4, & 5:

Carbon dioxide is absorbed by the

copper electrode

A free hydrogen ion is bound to one of

the carbon dioxide’s oxygens

The hydroxide unit detaches and meets

a hydrogen ion in solution to form water

The carbon atom fills its valence shell

by accumulating hydrogen ions from

solution

Step 6:

Step 7:

Step 8:

The CH3 unit detaches from the oxygen

atom and meets a fourth and final

hydrogen ion in solution to produce the

final product: methane (CH4)

The remaining oxygen attracts a free

hydrogen ion from solution

The hydroxide unit detaches from the

copper electrode and meets a hydrogen

ion in solution to form water

Ethanol (C2H5OH)

Enabling the Reaction----------------------------------------------------------------------------------------------------------------------------------

The left graph below is a graph of free energy for each step illustrated in the methane example considered before. If the change in free energy

from one step to another is positive (i.e. the free energy of a given step is larger than the previous step), the reaction will not be spontaneous. On

the left graph this occurs across multiple steps. This barrier can be combatted by supplying energy to the copper-carbon nanospike surface. With

enough energy, the change in free energy will decrease to a point where the reaction will proceed according to the right graph rather than the left

graph. For the right graph, all steps are spontaneous. The geometry of this surface dictates the magnitude of the energy applied that is necessary

for this process to proceed. As the reaction proceeds it becomes more and more difficult for the copper electrode to maintain its hold on the

molecule. The textured copper surface allows the copper atoms to have a stronger hold on the carbon dioxide molecules and promotes further

reactivity of the hydrocarbon. As the product of this reaction becomes more complex, the number of steps that this process must go through

increases. Research conducted by Lim et al. adds that as the complexity of the desired product molecule increases, the number of steps required

to create that product increases as well. Therefore, a greater energy is needed to ensure the spontaneity of the process. This is the limiting factor

of the viability of this process’ ability to be implemented for wide scale production of ethanol—as a complex molecule, the formation of ethanol

through this process requires a considerable amount of energy, which prevents this process from being energy efficient enough to be utilized.

Concluding Thoughts----------------------------------------------------------------------------------------------------

Overall this process has great potential to

change the world for the better; however,

due to the high energy input requirement,

the process is not yet energy efficient

enough to be put into wide scale use. There

is, however, potential to mitigate this issue

with the proper catalyst. Therefore,

considering the significant improvements

that this process could contribute to the

sustainability of emissions, energy, and

food supply management, further research

is necessary in order to make this method

of converting carbon dioxide to ethanol

viable in the future.

Added EnergyNo Added Energy